"In der Klamme" IS ON THE GRID
South Tyrol’s biggest private power station and one of the most exciting hydropower projects in Northern Italy in recent years: the “In der Klamme” power station was connected to the grid.
This was preceded by 18 months of intense construction work in which new territory was entered and new ideas were realised both in technological and ecological terms. Today this plant generates about 27 GWh of clean electricity a year.
Installing a power station in the vicinity of a nature reserve needs a very careful touch and a good concept. Especially when it’s a hydroelectric power station that led to some extremely controversial debate beforehand. But the plans developed by the planning bureau of Studio G in Bruneck had not been given the job over competitors’ projects for nothing. In the end the planners from Pustertal succeeded in reconciling economical eco-electricity generation with a high-quality solution in terms of ecology and landscape aesthetics. One proof of this is the power station, which has as far as possible been constructed underground, its front façade clad with local timber and the, finally, building “greened “ over with the earth that was retained. In the context of compensatory measures, a pond for amphibians and fish has been built in the immediate vicinity.
COOPERATION ON PLANNING
In accordance with the original plan, the water to drive the turbines is diverted from the Ahr in St. Peter, then conveyed via a 1,300 metre-long headrace tunnel and then via a 2,000 metre-long underground pressure pipe to the machine house. A complex headwater route whose planning and implementation was amongst the core challenges of the project.The contract for the specialist planning of the gallery construction and hydraulics and the specialist construction work was given to the BERNARD engineering planning bureau in Hall and to ÖBA Stollenbau. The South Tyrol planning bureau of Patscheider und Partner was commissioned for the structural design and supervision. The three planning bureaux succeeded magnificently in their collaboration. The optimum coordination provided the basis in the end for delivering the extensive construction work on time and within budget. The biggest part of the gallery excavation work was carried out with the aid of a 145 m-long tunnel boring machine. 24 October 2010 saw the breakthrough to the east portal – a real milestone in the power station project. After that, the construction work proceeded at a pace and even the frosty temperatures of winter 2010/2011 could not disrupt the project.
LAID IN THE TIGHTEST SPACE
The thing that fundamentally distinguishes this project is that most of the components have been installed underground and later integrated into the natural landscape. This of course applies first and foremost to the pressure pipe, the laying of which was a real challenge for the construction company engaged. Planner Dr. Ing. Anton Griessmair says on this: “High standards of precision and timing were set with the above-ground laying of the 3.90 m pipe in the gallery. In only 25 workdays, about 1,300 m of GRP pipe to DIN1800 were laid in the tightest space, with 300 m that had to be designed as curved.” In the gallery, the pipe was laid on prefabricated galvanised pipe supports. These supports themselves were used as drawbars for the insertion of the pipes in the gallery. The remaining 2 of the total of 3.3 kilometres of headwater piping was laid underground in the earth.
The double-chambered sand filtration unit constructed in a cavern in a cliff is also seenas a distinguishing feature of the plant, which has little of a standard solution about it. 9,500 m3 of a cliff had to be excavated for its construction. The sand trap is a good 83 metres long and it has been designed with a restriction in the shape of a 12.30 metre bottleneck. The complex transition from the intake to the sand trap in particular turned out to be a tricky matter for the planners. In addition to the aspect of proceeding in a way that would protect the landscape, the main reasons for moving the sand trap underground were the restricted space, local conditions and protection from possible avalanches. This method of construction also brings the benefit that it provides the best conditions for operating in the cold winter months. After installation of the pressure pipes, the old tunnel portal was filled in again with excavated material and earth, the landscape restored and matched to the existing landscape and once more prepared for future cultivation. After the rough site landscaping, the layer of soil that had been carefully carried away and temporarily stored was spread back over the site.
WITH THE GREATEST RESPECT FOR NATURE
A generous level of residual water is guaranteed so as to maintain the quality of the freshwater environment and fish biology in the outlet area. In line with the suggestions of the relevant state authorities of South Tyrol this provides a residual water outflow that is made up of a fixed proportion of 350 l/s over the fish ladder and a dynamic proportion of over 25 percent – calculated back from the apertures of the turbine jets – at the water intake. In addition to these mitigating measures, which included among other things the greatest possible protection of the landscape, the project managers also had to implement environmental compensation measures. The main focus of these was on concepts for creating additional environments for the aquatic and freshwater ecologies and thereby improving the quality of these areas. Both the removal and reshaping of obstacles to migration in the stream bed and the installation of waters for amphibians and spawning were therefore part of the design project. Indigenous trees and bushes were replanted in the bank areas.
In addition to the ecological and structural aspects of the power station one should also highlight the solutions that were implemented in hydraulic steel construction. Thus for instance the Tyrol Weir installed was equipped with an automatically operated return grille located underneath it. This prevents logjams in the through-flow grille. The individual screens are each cleaned from underneath with a kind of combing action using a hydraulically-operated return grille. The material “combed out” in this way is washed away with the water that flows away.
A FINE SET OF MACHINERY
At times of heavy water flow the new “In der Klamme” power station on the Tyrol Weircan take in up to 4.8 m3/s from the wild waters of the Ahr. The water hits the two six-jet vertical Pelton turbines with a pressure of about 17 bar. As a consequence, the planners and those responsible for the project gave the greatest attention to quality in the matter of electromechanical equipment. The two six-jet Pelton turbines come from the firm of Geppert in the Tyrol. They are designed to provide 7,315 kW each with a head of 176.35 metres and a water discharge flowrate of 4.8 m3/s. Nor is the generator solution of lesser quality. The two synchronous generators, whose rotor shafts are each directly linked to the turbine flywheels, come from the quality Austrian manufacturer ELIN Motoren GmbH. The generators from this motor specialist based in Weiz have without doubt been amongst the top firms in terms of the standards of their synchronous generators for hydropower for decades where efficiency, high level of availability and long life are concerned. The two synchronous generators convert the mechanical energy of the flywheel into electrical energy. They are designed to generate almost 5 MVA each. The electricity generated is fed via a 20 kV medium-voltage underground cable to a primary station in Mühlen in Taufers and from there into the 130 kV TERNA grid. In a normal year the new power station will generate a total of about 27 million kilowatt hours. Today, with this generating capacity, this new plant represents a new, important foundation stone for securing independence of supply in the Ahr valley in South Tyrol. In particular, with the constantly recurring power cuts in the interregional grid, this power station acquires great importance.
A LONG PREHISTORY BUT A SHORT CONSTRUCTION TIME
Back in 2002, Ahr Energie GmbH, which was owned by its president Dr. Karl Hellweger and 10 Ahr valley residents and firms, submitted a project to obtain the water concession for electricity production. In 2004 the environmental impact assessment proved positive. Over the following five years to 2009, the project had to be defended against other, competing projects. Several legal actions were required. In the end, Ahr Energie GmbH, the victor in this competitive situation, was able to start on the construction work for the power station in the spring of 2010. The plant was ready to operate in July 2011 and was able to supply the public grid from the start of September 2011.
The entire project was mainly formulated and supported from start to finish by Dr. Ing. Anton Griessmair’s Studio G engineering bureau in Bruneck and, in collaboration with specialist bureaux and technicians, it was finally prepared for implementation and supported during construction. A large part of the project development and construction supervision, especially in the fields of tunnel construction and water hydraulics, was in the hands of the BERNARD bureau of engineers in Hall in the Tyrol and the structural design was in the hands of the Patscheider & Partner engineering bureau in Mals im Vinschgau. The landscape ecology construction support and the implementation of the compensatory and mitigating measures were carried out by the TRIFOLIUM bureau of landscape ecology.